Table 1 Studies reporting supine awake vs. supine with reduced consciousness

Safar et al. [25] (1959) USA

80 adult volunteers, no lung- or airway disease

Interventional study of airway patency under general anesthesia, placing the volunteers in various supine and prone positions. For the purpose of our study: Supine, awake vs. supine, anesthetized. Outcome: open, partially obstructed and obstructed airway.

Incidence of obstruction:

No p-value given.

• Supine, awake: 0%; anesthetized: 54% partially obstructed, 36% obstructed, 10% open airway

Loss of airway patency when going from awake to general anesthesia in the supine position.

Kopelman et al. [26] (1986) England

40 adult male volunteers, 20 obese, 20 normal weight

Observational study of oxygen saturation while awake and during sleep, both in supine position.

Minimum S_aO₂, mean (%):

p < 0.01 for both comparisons.

• Obese group: Supine, awake: 96, asleep: 80

Shows lower oxygen saturation asleep in the supine position vs. awake, most profound in the obese group.

• Normal weight group: Supine, awake: 97, asleep: 94

Ikeda et al. [27] (2006) Japan

14 healthy adult male volunteers

Observational study on airway collapsibility under midazolam sedation in supine position vs. 30 degrees elevated upper body. Outcome is critical closing pressure of upper airway (P_crit)

P_crit, mean, cmH₂O (SE):

p < 0.05.

• Elevated upper body: −13.2 (1.3)

Critical closing pressure of upper airway may be regarded as a measure of patency of the airway; the lower supine value means increased collapsibility.

• Supine: −8.2 (1.4)

Lee et al. [28] (2009) Taiwan

48 adult patients, 28 with obstructive sleep apnea (OSA).

Observational study on work of breathing (WOB) in supine position, asleep and awake. Reports data in three OSA groups and control group.

WOB, mean, J/l:

p < 0.05 for all comparisons.

• Control group: Supine, awake: 0.70, asleep: 1.16

An increased WOB may be an indicator of airway obstruction, but no firm conclusion should be drawn from this study.

• Eucapnic, non-obese group: Supine, awake: 1.20, asleep: 2.07

• Eucapnic, obese group: Supine, awake: 1.41, asleep: 2.25

• Hypercapnic group: Supine, awake: 2.27, asleep: 3.13

Tagaito et al. [29] (2010) Japan

9 male patients with OSA

Interventional study of upper airway closing pressure during general anesthesia and sitting vs. supine position. P_close is estimated on to levels of the upper airway.

Airway closing pressure, P_close, median, cmH₂O:

p < 0.01 for both comparisons.

• Retropalatal airway: Sitting: −3.47, supine: 2.20

Airway closing pressure may be regarded as a measure of patency of airway; the lower values in the supine group mean increased collapsibility.

• Retroglossal airway: Sitting: −5.31, supine: 2.67